


the job of a big brother

by oikawakkun



Series: HQ Angst Week 2020 [3]
Category: Haikyuu!!
Genre: Alternate Universe - Kimetsu no Yaiba Setting, Angst and Hurt/Comfort, Blood and Injury, Character Death, Day 3 - all the tiers, Gen, Haikyuu Angst Week 2020, Platonic Relationships, Rated For Violence, Reincarnation, This is really sad, im sorry, my first rated m and it's miya twins angst, no beta we just die
Language: English
Status: Completed
Published: 2020-11-03
Updated: 2020-11-03
Packaged: 2021-03-09 00:47:47
Rating: Mature
Warnings: Major Character Death
Chapters: 1
Words: 2,350
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/27366052
Author URL: https://archiveofourown.org/users/oikawakkun/pseuds/oikawakkun
Summary: There’s no other love like the love for a big brother. There’s no other love like the love from a big brother.Atsumu would do whatever it takes to protect the both of them.
Relationships: Miya Atsumu & Miya Osamu
Series: HQ Angst Week 2020 [3]
Series URL: https://archiveofourown.org/series/1998721
Comments: 8
Kudos: 87





	the job of a big brother

**Author's Note:**

> Day 3 - photographs + defeat + "i can't lose you too."
> 
> (this fic was just me being very self indulgent by making tiny ten year old Osamu call his big bro 'Atsumu-nii")
> 
> all three tiers gave me the inspo to finally try a kny au for the miya twins :') i'm sure JJ would be into this au so think of this as an early bday present from me !!! also, i'm not too confident when it comes to fight scenes (so i tried to avoid it as much as i can) im hoping i didn't end up butchering this fic for yall lmao

_“Sibling relationships outlast marriages, survive the death of parents, resurface after quarrels that would sink any friendship._

_They flourish in a thousand incarnations of closeness and distance, warmth, loyalty and distrust.”_

― **_Erica E. Goode_**

* * *

They just wanted to see their mother's smile again.

 _Bronchitis._ They were told of her terminal illness and the doctors couldn't do anything about it. Their sweet and lovely mother was dying right in front of their eyes and they couldn't do anything about it. Osamu was shaking with grief, the feeling of helplessness clinging to his chest as heavy sobs made its way out of his trembling lips. 

_Why does it have to be their mother?_

Their father couldn't bare to look at her pained face but Atsumu-nii stood his ground as they stayed right by her bed, his face was hard as stone and his cheeks were free of tears. He held Osamu's hand in a tight grip, grounding Osamu as he finally let his tears fall freely from his face, knowing that his big brother will be there for him.

She didn't have much time left and their father was too caring― too desperate.

He left the following evening in hopes of fetching some medicinal herbs near the mountain.

_They all knew the herbs wouldn't work._

Atsumu was adamant to make him stay. The two of them fought the entire night and Osamu wasn't able to do anything but watch as Atsumu stormed off to his room when his father closed the door and headed off to the mountain during a storm.

The trail was dim and slippery that night, their father ended up falling off a cliff to his death.

Atsumu had to tell him the news the following day, his eyes red rimmed and his voice barely a whisper.

Their mother didn't make it the following day and Atsumu had to drag Osamu off her bed kicking and screaming in order to burry their mother's decaying body at the back of their house, right next to their father's grave.

Atsumu doesn't talk much after that.

* * *

Atsumu started taking over their father's business a few days after.

Cutting down wood to sell to the village, his small body working from morning until the late afternoon. He never asked for Osamu's help, no matter how many times he tried to offer. Atsumu was quick to shut him down with a glare and a short "Listen to your Nii-san" as he pushed Osamu inside their house to make lunch.

This became their new routine until the following spring.

Osamu missed the warmth of their house.

Osamu missed his older brother.

* * *

The following spring, they meet a woman named Amane Ubuyashiki.

She was very pretty. Osamu thought she was a spirit of a white birch the first time he saw her.

She told them of stories from long ago. Of demons and swordsmen. Of a strength in a breath that Osamu has never heard of before. She said they were the descendants of those very same swordsmen― the ones who could use the first ever breath.

Atsumu was quick to throw her out of their home.

Anger making his voice crack as he told her to leave and never come back. Osamu has never seen his older brother this angry before, not even when he shouted at their father for leaving.

Amane Ubuyashiki left with a graceful bow and Osamu was left wondering what it would be like if they became swordsmen together.

He voiced out his thoughts during dinner that evening.

Atsumu got really quiet after that and Osamu was about to ask him what was wrong when he hears a loud thud, Atsumu slamming his bowl on the table too hard that it cracked.

"Don't be an idiot, 'Samu!" Atsumu started, his glare was harsh and unforgiving as he looked at Osamu's gray eyes with his own piercing gaze. "We're just fuckin' children! Left alone by a stupid old man who loved his dying wife more than his own two kids!"

"Don't say that about them! Ma and Pa loved us!" Osamu didn't know why Atsumu was saying these things, anger made him shout back. "Ubuyashiki-san was just trying to offer us another way out of this empty house!"

"That woman is just going to use us, 'Samu!" Atsumu shouted, just as angry. "She's probably planning something. We're done talking about this, so shut up and eat yer food!"

They stopped talking after that.

* * *

Amane-sama kept coming back to their house.

Atsumu started closing the door on her face and shouting curses at her every time she visited.

"Stop botherin' us and go find a different pair of kids to send to their early graves!" 

Osamu doesn't even flinch when the door slammed too hard, the echoes vibrating in their empty home.

* * *

Summer finally came.

The heat was still sweltering despite the late afternoon, with an almost choking feeling that Osamu hates with a passion.

He's still mad at Atsumu.

They barely talk anymore.

The summer night was just as hot and the cries of cicadas could be heard from the distance.

Atsumu was still working for the two of them on his own, still so quiet and angry, and Osamu doesn't know how he'll ever be able to get his old Nii-san back.

_Why did this have to happen to them?_

* * *

That night, the door opened while they were sleeping.

A demon came in.

Its eyes were glowing red and its presence full of malice and hunger sent a chill down Osamu's spine. Atsumu was already up with an axe before Osamu could register what his big brother was doing.

A scream.

Atsumu was screaming and clutching his side and Osamu felt something thud right next to him, he looks down and the bloody sight made his eyes widen. Atsumu's left arm was laying on the wooden floor, blood slowly crept until it was covering Osamu's feet.

"Shut up! Shut up! Shut up!" The demon screamed, "Yer nothin' but a bunch of pathetic kids living alone. Just die."

Atsumu was holding Osamu with his remaining arm, hard and tight, trying his best to hide him from the demon's sight.

"Don't hurt him!" Atsumu shouted protectively. "You can do whatever ya want with me, just don't hurt my little brother."

The demon looked at Atsumu with a sneer, then his crimson eyes shifted to Osamu and the demon started to laugh. The sound was something Osamu would never forget, loud and taunting, so full of bloodlust that Osamu's heart shook in his chest.

"A mere child shouldn't be making deals with a demon." The monster started, "Your lives mean nothing to me. Whether you live or not, nothing changes."

After hearing the demon's heartless words, Osamu felt something shift within him.

Something bubbled at the very pit of his stomach, an intense anger that he's never felt before. Fueled by such an intense emotion, Osamu broke from Atsumu's grip with a scream of his own as he tackled the demon with the axe laying on the floor.

The fight was lead outside until they reached their yard. The events after that was a blur of red for Osamu, and all he could remember was the feeling of bones cracking and constant slicing of flesh. And the awful scent of blood. There was so much _blood._

When Osamu finally came back to his senses, the fight was already finished.

The demon was so close to death, its head crushed by a heavy stone yet its body refused to stop moving. It's still struggling for life and Osamu watched in horror as its limbs tried to regrow. but the morning sun finally came up, and with its light, the demon crumbled to dust.

Osamu didn't care about any of that. He just wanted to go back to Atsumu.

He wanted to tell his big brother what happened, that he was safe and he didn't have to worry about Osamu anymore. But his body felt so heavy. It took him several hours to get to the front door, his body crawling from exhaustion. 

He spots Atsumu at the same place he left him that night and the sight made Osamu want to vomit the contents of last night's dinner.

Blood. _There was so much blood._

Atsumu was laying face down, his face barely visible from all the red, he's panting heavily, saying something Osamu couldn't quite hear from their distance.

Osamu wanted to say his name, to get his attention, but his voice wouldn't come out. 

His throat was hurting so much.

Osamu pushed his body forward, ignoring the strain in his muscles and the pain from the wounds on his legs. He needs to get to Atsumu.

He needs to get to his big brother.

"Dear gods... Buddha, please..." Atsumu was chanting, his voice barely a whisper. "Please... spare my little brother... unlike me, he's really kind... He just wanted to be useful... and I got in his way..." Atsumu was sobbing now, his tears mixing in with the blood on the floor.

This is the first time Osamu has ever seen his brother cry.

Not once did his older brother shed a single tear when their mother and father passed away, not even when they had to bury them on their own.

But Atsumu's entire body was shaking with heavy tears as he prayed to any god who would listen. "If yer gonna punish someone, just give it all to me.... he's my only little brother." Atsumu pleaded to the air.

"Ya... ya can't take him from me too."

Osamu finally got to reach for Atsumu's hand, it was too cold to the touch and Osamu wanted to scream his name. _'I_ _'m right here Atsumu-nii. 'Samu's right here with you.'_

_No. No. No. Not Atsumu, please don't take him from me too. I can't lose him too._

Atsumu released one last shaky breath and his chest stopped rising after that.

Osamu sobbed as he held onto Atsumu's limp hand.

* * *

Three years later and Osamu is now the current Mist Pillar.

His _Nichirin Blade_ gleams in the moonlight as he strikes down every demon in sight.

_"If you ever do something to help others, 'Samu. Always remember that the 治 in Osamu, means to rule. Hold your chin up high and never let grief weight you down."_

* * *

Osamu is dead.

Defeated by the first upper moon demon.

When Osamu opened his eyes, he is greeted by Atsumu's own.

"Nii-san?"

Atsumu's face is full of grief and his tears won't stop falling from his eyes. "Stay away!" he shouted, his voice cracking at each syllable.

"Go back, 'Samu!"

"Why? I tried so hard... you're not even proud of me?" Osamu felt his heart breaking all over again.

"Why, ya ask," Atsumu muttered to himself, "That's what I wanna know. Ya should've just ran away from that demon. Yer only fourteen!"

"But my friends would've died." Osamu answered, "I can't just abandon them!"

"But you died, 'Samu!" Atsumu's voice shook and it's probably the first time Osamu ever heard his brother sound this broken. "What's the point of dying in a place like this? Why even be born then?" 

"You died at eleven! You left me alone so you can't say that to me!" Osamu was crying now.

"I was born to be happy." He adds later on, his voice a lot softer.

"I was born with a happy family, I grew up with friends who loved me... So don't say it was all for nothing." Osamu sobbed, "Other people can say whatever they want, but I don't want my brother to say something like that. Not when you gave up your life for me!"

Osamu felt two strong hands grip his shoulders, Atsumu was resting his forehead on his own and Osamu could feel Atsumu's tears dripping on his cheeks. "I understand... M'sorry 'Samu..." Atsmu was whispering, holding Osamu so tightly like he's scared he'd disappear if he didn't hold onto him hard enough.

"I get it... But..." Atsumu said, "I didn't want ya to die, 'Samu."

"Anyone but you."

Osamu just held onto him tighter as he cried his heart out, finally letting his tears fall freely from his face, knowing that his big brother will _always_ be there for him.

Even death could never keep them apart.

* * *

_**Present Day** _

Atsumu is five years old when he stumbled upon an old photograph in their attic.

It showed a bunch of faces he doesn't recognize, but he sees a short boy standing by the side that looked a lot like him and 'Samu . He showed the photo to his brother and they both asked their mother who it was during dinner that evening.

Their mother smiled easily, telling them an old story full of demons and swordsmen with blades so sharp it could cut a boulder in half.

Atsumu thought the story sounded weird but Osamu was more than happy to listen to their mother talk about their ancestors some more.

Dinner ended and they both made their way to bed.

That night, Atsumu dreamt of the same demon in his mother's story, red eyes glowing in the moonlight and claws as sharp as steel. The dream was too vivid― almost like a memory from long ago.

Atsumu wakes up with unshed tears and a soft "Don't hurt him."

Osamu wakes up from Atsumu's thrashing and easily crawls right next to Atsumu, his small protective arms wrapping around Atsumu like the safest blanket in the world. "Go to sleep, Atsumu-nii. I'm right here." Osamu says softly and in the next few seconds after that, Osamu's already fast asleep.

With an exasperated sigh, Atsumu gives him a pat on the head as he tried to move a bit closer to Osamu, placing the blanket over the two of them as he got himself ready for sleep once again.

"Stupid, Osamu." Atsumu thought, laughing fondly. "Older brothers should be the ones protecting their little brothers. Not the other way around."

They both fell asleep in each other's arms with a happy content smile on both their faces.

**Author's Note:**

> this fic was so painful to write, i was sobbing the entire time ngl !! i was up all night thinking about how i'll be able to make this really painful for everyone (including myself) anyway, kudos and comments give me life :D


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